ZXR250C or CBE250RR questions

[bawked]

So I've ended up with both a ZXR250C and a MC22 CBR

ZXR:

My zxr started running poorly and not revving past 12k rpm, was sent down to hamilton for work for a couple months so dropped it into cycletreads. A $1000 later, I have a bike that still runs shit.... apparently due to over worn emulsion tubes. I'm dubious as it runs poorly up at the 12k+ rpm range at full throttle, where the main jet should be doing the work. I managed to sort another set of carbs for cheap though, so I'm planning on testing them with the stock jetting to see if the situation is improved.

I have an aftermarket pipe that I imported from overseas, but if i use it I should probably up the mains jets one size. Who is the best person to talk to regarding carbs parts, such as jets and rebuild kits.

Also since it is a 250 i'm sure no one would've checked the valve clearances, who in auckland sells shims?

CBR:

The bike seems to pull smoothly through the rev range, but one thing that I have noticed is a small hesitation below 3k rpm. It's not really a problem, just annoying when taking off from the lights. It bogs, then takes off as soon as the revs have picked up a little. The bike has an aftermarket pipe on it, but I doubt that would affect fueling all the way down there. Sounds like an oversized pilot jet I think?

Also I'll check the valve clearance on this as well.

I relatively new to the whole carb tuning, I've done a efi tuning course and setup a gsxr600 engine with a link g4 storm. But this is a different ball game, so some guidance would be much appreciated.

[nzspokes]

I know a bit about carbs, so ask at the next Sass.

It will be worn needle seats, talk to this guy. Alec. Chances are if he dont have them he can make em. He is in Whitford. I had the same problem on a Kawasaki and was told at a dealership to get new carbs. I got seats from Alec for $10 each I think it was.

[bawked]

I had a chat to Alec, he recommended boring out the emulsion tubes and getting new needles made. I may do that anyway, as we have a mill at work... Getting new needles made will be a different story, might have to get a CNC place to make some on a lathe

[Tazz]

Got a vid of the CBR hesitation? Maybe it's not normal but mine is also like that (not in a way I'd complain about though so yours may be worse, I just thought it made sense considering the rev range. I wouldn't be expecting much power down low considering these rev out to 18k...).
I just ease the throttle on when that low (usually only when I haven't bothered changing down a gear/3) or just keep the revs up when pulling off... You can have them at 8-12k without sounding like you're wanting to race everyone in slow motion.

Sweet spot seems to be from about 10k and mine cruises between 10-12k around 100-120 from memory.

[FJRider]

Got a vid of the CBR hesitation? Maybe it's not normal but mine is also like that (not in a way I'd complain about though so yours may be worse, I just thought it made sense considering the rev range. I wouldn't be expecting much power down low considering these rev out to 18k...).
I just ease the throttle on when that low (usually only when I haven't bothered changing down a gear/3) or just keep the revs up when pulling off... You can have them at 8-12k without sounding like you're wanting to race everyone in slow motion.

Sweet spot seems to be from about 10k and mine cruises between 10-12k around 100-120 from memory.

I agree ...

For a bike that rev's out to 18K .. 3K is not far above stalling ....

[nzspokes]

I would have to guess a blocked idle jet.

[ducatilover]

ZXR:
Runs like shit? Can you elaborate?
You can buy the emulsion tubes from overseas, don't buy second hand carbs :facepalm:
For a basic slip on can, pull the jets out of cyls 2/3 (122 I think, from memory) and chuck them in to numbers 1/4, then buy the size up from Nikau on trademe, for $6 each.

CBR, hesitation under 3k?
This all depends on load and throttle position, so can't really say over teh internets.
But I would look at doing a carb sync, then a set of plugs. Because it's cheap and it's nice to pamper your bitch.
Check the air filter, intake boots etc etc etc
After these you can go set the carbs up.
Or you could just not be used to having a small 4cyl (mind you, my Bandit pulled from any revs with no flatspots and made 45hp too, could load it up in 6th from 2lrpm without flatspots)

Edit, just read you have an aftermarket pipe.
Does it go flat feeling and hollow sounding or "wet" feeling

[ducatilover]

I agree ...

For a bike that rev's out to 18K .. 3K is not far above stalling ....

I've set carbs up on a few and they never have flatspots. You just have to have all your ducks in a row, as with any engine :msn-wink:

3k is still 1.5k above stalling and shouldn't be flatspotting

[bawked]

ZXR:
Runs like shit? Can you elaborate?
You can buy the emulsion tubes from overseas, don't buy second hand carbs :facepalm:
For a basic slip on can, pull the jets out of cyls 2/3 (122 I think, from memory) and chuck them in to numbers 1/4, then buy the size up from Nikau on trademe, for $6 each.

CBR, hesitation under 3k?
This all depends on load and throttle position, so can't really say over teh internets.
But I would look at doing a carb sync, then a set of plugs. Because it's cheap and it's nice to pamper your bitch.
Check the air filter, intake boots etc etc etc
After these you can go set the carbs up.
Or you could just not be used to having a small 4cyl (mind you, my Bandit pulled from any revs with no flatspots and made 45hp too, could load it up in 6th from 2lrpm without flatspots)

Edit, just read you have an aftermarket pipe.
Does it go flat feeling and hollow sounding or "wet" feeling

Well the zxr runs nice down low, at 12k and 16k rpm though it has huge dead spots. Between the dead spots it is really nice, and pulls hard. The guy at cycletreads put 2 sizes smaller jets on the inside, and one size smaller on the outside... And he suggested going another size smaller (115) on the insides.

Where can you get replacement emulsion tubes?! That is want I wanted, but everyone says you cant buy them, since they aren't replaceable.

I'll give the CBR a pampering, and see if the issue still remains. My zxr pulls smoothly from 1k rpm all day, so the CBR should as well.

[ducatilover]

Well the zxr runs nice down low, at 12k and 16k rpm though it has huge dead spots. Between the dead spots it is really nice, and pulls hard. The guy at cycletreads put 2 sizes smaller jets on the inside, and one size smaller on the outside... And he suggested going another size smaller (115) on the insides.

Where can you get replacement emulsion tubes?! That is want I wanted, but everyone says you cant buy them, since they aren't replaceable.

I'll give the CBR a pampering, and see if the issue still remains. My zxr pulls smoothly from 1k rpm all day, so the CBR should as well.

Err... smaller jets? :blink: Fuck that.
I have a mate that reckons he did his recently, will flick him a message and get back to you

Has anyone actually checked the emulsion tubes are fucked? Or just making assumptions

And has the ZXR got a standard exhaust/filter?

[mossy1200]

I'll give the CBR a pampering, and see if the issue still remains. My zxr pulls smoothly from 1k rpm all day, so the CBR should as well.

Don't think mine would like 1k. That's almost idle.
Wouldn't most 250 fours be 3k to leave from stationary.
My bike seems to launch best at 7k. I can putter off at 2k ok if there is a cage in front of me.

[ducatilover]

The majority of 250/4s will tootle off 2k cleanly if they have all their ducks in a row.

Which is insane when you look at their lobe center and duration numbers, says something about rod-stroke ratio and sexy head flow...
But this is KB, so your bike is normal. Or fucked

[FJRider]

The majority of 250/4s will tootle off 2k cleanly if they have all their ducks in a row.

Which is insane when you look at their lobe center and duration numbers, says something about rod-stroke ratio and sexy head flow...
But this is KB, so your bike is normal. Or fucked

And the majority of those 250/4's owned by site members are NOT new ... and have six figure speedometer readings.

Nothing was mentioned in the first post of this thread ... on the age or distance traveled .. of either bike.

[ducatilover]

And the majority of those 250/4's owned by site members are NOT new ... and have six figure speedometer readings.

Nothing was mentioned in the first post of this thread ... on the age or distance traveled .. of either bike.

Which is why ducks should be in rows :yes: as with any machine

[bawked]

Which is why ducks should be in rows :yes: as with any machine

This is very true, if every part of the engine is up to spec then there is no reason why it won't run well. Just because an engine has 100,000+ km doesn't mean it's shit.

I bought a second hand set of carbs, to quickly rule out the emulsion tubes. Also if I need to bore them out I'd rather have a spare set, to use as a control/backup. Turns out the set I bought had bigger jets, so don't have to worry about getting them either. And they were cheap as chips.

Took the cbr out for a good ride today and apart from the issue at low rpm, it pulls like a beast. Puts the zxr to shame I think.

[ducatilover]

:2thumbsup Chur, keep us updated.

[FJRider]

This is very true, if every part of the engine is up to spec then there is no reason why it won't run well. Just because an engine has 100,000+ km doesn't mean it's shit.

At 100,000 km's (over or near) ... without the internals being touched ... odds are it is shit.

ie: Compression is down ... it's using oil ... and it's getting harder to start. (Have YOU checked the compression on both bikes lately .. ??)


I bought a second hand set of carbs, to quickly rule out the emulsion tubes. Also if I need to bore them out I'd rather have a spare set, to use as a control/backup. Turns out the set I bought had bigger jets, so don't have to worry about getting them either. And they were cheap as chips.

If that model worked well with the original sized jets ... why the need to replace with a larger size now ... ??


Took the cbr out for a good ride today and apart from the issue at low rpm, it pulls like a beast. Puts the zxr to shame I think.

Don't let the revs drop below 4000 rpm. (on either bike) The result may surprise you ...

[bawked]

At 100,000 km's (over or near) ... without the internals being touched ... odds are it is shit.

ie: Compression is down ... it's using oil ... and it's getting harder to start. (Have YOU checked the compression on both bikes lately .. ??)


If that model worked well with the original sized jets ... why the need to replace with a larger size now ... ??


Don't let the revs drop below 4000 rpm. (on either bike) The result may surprise you ...

1. I didn't say this wasn't the case, you were just over generalising.

2. Because air filter + straight thru can.... Combustion works by mixing a certain ratio of air and fuel, compressing and igniting. My bike with these will flow more air, hence I need to flow proportionately more fuel to maintain correct fueling.

3. It won't surprise me, I've had my bikes over 4k rpm before :facepalm:


So I pulled the carbs off my ZXR tonight, was going to just slap the other carbs on it and see how it goes. But decided I should check valve clearances, balance the carbs and do a compression test while I'm at it. I'm betting no one has looked at the clearances in ages and they are miles out, 250's don't seem to get much love.

So seems the needle jets are a tad worn, the beastie below being the worst. The outter two were actually in decent nick. The needle jets in the replacement carbs I have are all in better nick than the outter ones of these so that's a good start at least.

305035

So guys, this is why i'll never take my bike to cycletreads again... they machined the caps of my needles down without asking me :facepalm: and did a fucking rough job of it at that. Apparently since the emulsion tubes were ovalised, they over fueled so lowering the needles helps neutralise this... but still, who the hell does this sort of shit?!

305034

The stock main jets on 1 & 4 are 122, 2 & 3 are 125. The below is what my bike came back with... and with the recommendation to try go down to 115s on 2 & 3 to try get rid of the hesitations.

305032

In the intake box there was no filter.... just this shitty mesh looking thing. I see that people recommend unifilters for the cbrs, is this the case for the zxr? They seem to be cheap as chips.

305033

Does anyone have a carb balancer I could borrow, nz being nz I assume I'd have to import one.... which i will do eventually.

[nzspokes]

That gauze looks like a backfire guard. No air cleaner? I would get a stock one to get the bike back to basics. Higher airflow ones just mean more mucking about getting the jetting right. Some motors produce less power with a high flow filter.

Have you looked into getting some needle jets turned up? Or even for a rough fix brazing yours up and re-drilling them?

I have a Carbtune balancer, but i come with it. I dont lend tools but happy to pop over with it when your ready with it.

[bawked]

That gauze looks like a backfire guard. No air cleaner? I would get a stock one to get the bike back to basics. Higher airflow ones just mean more mucking about getting the jetting right. Some motors produce less power with a high flow filter.

Have you looked into getting some needle jets turned up? Or even for a rough fix brazing yours up and re-drilling them?

I have a Carbtune balancer, but i come with it. I dont lend tools but happy to pop over with it when your ready with it.

I'm sure I had a filter in there from when I replaced my throttle cable, maybe cycletreads took it out and forgot to put it back in... I got a second hand set of carbs which have much better looking needle jets, so i'll use those as my base.
Sounds fair enough, i'll let you know when I'm good to go.

[ducatilover]

If the spare emulsion tubes are betterer use 'em with the corresponding needles, go with stock jet sizes, make a uni-foam filter of buy one, don't go pods. Then re-jet to suit.
The smaller jets installed with decent emulsion tubes and needles will be insanely lean
Lowering the needle won't fix an out round hole, this makes me LOL. Only way to fix is replace, or solder and re-dril. But to drill and ream one to the right specs is another story all together

One hori as fuck thing you can do is lap the old needle and seat in. But with your spares, there's no need. The other is to drill out the ovalisation (is that even a word) and use the lowered needles

[ducatilover]

Oh and build a manometer, best carb sync tool you can buy and it costs bugger all to make :yes:

[bawked]

Ok will get a filter, and some 122 jets so I can start with everything stock and go from there.

Finished work late today, so only managed to take the radiator off and barely started checking the valve clearances before it got too dark. It seems that the clearances are really really tight though, its hard to judge how tight though.. as the super thin feelers are not stiff enough to slide between the cam and seat easily. But I couldn't even slide .063 under them so which means they are at least .10 mm tight. Some I could slide a .406 under, so they are massively off as well :brick:

I'm guessing that if I did a compression test 2 & 3 will be low as the valves aren't fully closing, so that's on tomorrows agenda. Then i'll finish measuring up the clearances and get some new shims... might take a couple iterations if I can't measure the gap under some of them. Hopefully it was just due to the dark and not being able to see what i was doing though :sweatdrop

Also saw some cam rub marks on the valve cover, looks like it has good tension now... so must've had the chain and/or tensioner replaced at some point.

[ducatilover]

Yeah they tend to get tight in the valves as the seats recess, not uncommon at all and they do it faster when you run them lean :pinch:

[bawked]

Ah that makes sense, lucky I haven't burnt a valve I think.

Looking at the plugs only one cylinder was rich, the one with the very worn emulsion tube. For shits and gigs I might put a 115 jet only in that carb to see how it runs.

[ducatilover]

:shutup: Personally I wouldn't do that

[nzspokes]

Ah that makes sense, lucky I haven't burnt a valve I think.

Looking at the plugs only one cylinder was rich, the one with the very worn emulsion tube. For shits and gigs I might put a 115 jet only in that carb to see how it runs.

Problem is at WOT the motor is still very lean if you do that. Things can melt.

[bawked]

:shutup: Personally I wouldn't do that

Haha fair enough, I probably won't either since I want to get this running nicely quickly, so I can give my cbr some love before summer.

Seems the clearances weren't as bad as thought, well only 2/16 were in spec. But they aren't as far out as suspected, seems seeing what you are doing is a big help :yes:

Calculated what shims I need so hopefully I can pick them up tomorrow, slap em in on sat, and bolt the beast up ready for syncing and a test ride. :Punk:

[FJRider]

Looking at the plugs only one cylinder was rich, the one with the very worn emulsion tube.

For one with so much knowledge ... you ask many questions ... :shifty:

With NO air filter ... they'll all be running lean ... <_<


For shits and gigs I might put a 115 jet only in that carb to see how it runs.

Go for it ... what possible (more) harm/damage could it do .... <_<

[ducatilover]

For one with so much knowledge ... you ask many questions ... :shifty:

With NO air filter ... they'll all be running lean ... <_<



Go for it ... what possible (more) harm/damage could it do .... <_<

Worn emulsion tubes will be making it pig rich in the low and mid range, and possibly a little rich right up top (if you could get the fucker to rev that high with the tubes) so going down many jet sizes may help the transition up the needle, but right up top it's probabl lean off again
So, the plugs can read rich. But chances are the 12k+ rpm range will start getting back towards normal/lean.

[bawked]

It runs nice down low, there are no issues until 12k rpm onwards. It's very strange, I would've thought the worn emulsion tubes would've screwed up the midrange more and not so much the top end. I guess the proportion of the total fueling from the needles is quite high, otherwise it wouldn't be an issue.

I guess that's the interesting thing about carbs, fuel is supplied through all these different paths in different proportions throughout the rev range to maintain the right air-fuel ratios. And its all mechanical, amazing really.

[bawked]

Shims are $10 -> $12 EACH from motocycle shops ?!?

shit is insane, that means a $110 bill for me since I need so many.... unless someone knows of a cheaper place?

[bogan]

Shims are $10 -> $12 EACH from motocycle shops ?!?

shit is insane, that means a $110 bill for me since I need so many.... unless someone knows of a cheaper place?

What are the dimensions of the stack? I can turn up a single shim to spec'd height easy enough.

[ducatilover]

Bit of elbow grease and some very fine paper and you can sand your own ;) might need a decent vernier or micrometer though
I do it when I can and on a piece of glass.
Or get the real pro fulla to make em

[bogan]

Bit of elbow grease and some very fine paper and you can sand your own ;) might need a decent vernier or micrometer though
I do it when I can and on a piece of glass.
Or get the real pro fulla to make em

How do you sand the hole into the middle of it :scratch:

Also, what actually needs to be hitted with the hammers? few-mm-ish needle shims for like the 375 carbs per cc these 2fiddys have?

[bawked]

Found some cheaper shims, put them in.... within spec now.

Was assembling the bike and noticed the chain tensioner screw is shagged, same with a couple of carb airbox mounting threads :brick: I think its time for a ride on the cbr and I'll just have to drill and retap the holes tomorrow.

Also seems like the cam chain needs replacing, as it has tight and loose portions as I crank the motor over. But i'm moving house in the next couple weeks hence the hurry to get this thing back together. I'll order one and put it in once i have a nice garage to work in.

[ducatilover]

How do you sand the hole into the middle of it :scratch:

Also, what actually needs to be hitted with the hammers? few-mm-ish needle shims for like the 375 carbs per cc these 2fiddys have?

You're thinking of needle shims and I'm thinking of valvetrain shims?
Better shimmy along then.


Luckily cam chains are still available from Kawasaki :yes: